Where is the engine serial number on a VW bug?

Answer 1

On "Type 1" engines (Beetles and pre`72 US-market Buses) it's stamped in the rear of the case, just below the generator/alternator pedestal. "Type 3" (Fastbacks/Squarebacks/Notchbacks) cases have it stamped on the top of the case, alongside the parting line in the center. "Type 4" (411/412 and `72-up Buses in the US) have it both on the engine case and on the cast-aluminum fan shroud (which can be transferred from one engine to another and should therefore not be considered definitive).

There are many replacement cases out there (mostly Type 1 or 3) which have no I.D. number anywhere - their vintage can be determined by the casting numbers on the side of the sump and physical characteristics (things like the number of oil pressure control valves and the diameter of the oil pump studs - head stud diameter is not a reliable indicator since it's not uncommon for them to be replaced and/or steel thread inserts installed where they screw into the case). And "Factory Exchange" cases exist which have had their original serial number milled away and a new one stamped into the resultant cartouche; there were also aftemarket rebuilders who would rivet their own I.D. plate over the original number. On these, the codeletter represents the configuration of the latest incarnation, not necessarily what the case was used for originally.